Because typical LCD devices have the advantages of portability, low power consumption, and low radiation, they have been widely used in various portable information products such as notebooks, personal digital assistants (PDAs), video cameras, and the like. Furthermore, LCD devices are considered by many to have the potential to completely replace CRT (cathode ray tube) monitors and televisions. On the other hand, the display mode of typical LCD devices is hold-type, and the response speed of liquid crystal molecules employed in such LCD devices may be too slow. As a result, the residual image phenomenon may occur when motion pictures are displayed on LCD devices.
In order to solve the above-described problems, a typical method employed for eliminating the residual image of LCD devices is the so-called black image insertion method. In the black image insertion method, a frame is divided into a first sub-frame for displaying the actual image and a second sub-frame for displaying a black image. However, because a black image is displayed between every two actual images, a viewer may easily perceive a flicker phenomenon. Furthermore, because a black image is displayed in each second sub-frame, the brightness of the images displayed by the LCD device is correspondingly reduced.
Referring to FIG. 4, a typical LCD 1 configured for eliminating the above-described problems of flicker and low brightness is shown. The LCD 1 includes a driving circuit 10 and an LCD panel 14. The driving circuit 10 includes a frame memory 11, a comparator 12, and a gradation processor 13. The frame memory 11 has a plurality of gradations V(m) of a number m (0≦m≦59, m is a natural number) frame pre-stored therein. The frame memory 11 provides the gradations V(m) of the number m frame to the comparator 12. After the gradations V(m) are provided to the comparator 12, the frame memory 11 receives a plurality of gradations V(m+1) of a number m+1 frame and stores the gradations V(m+1) therein.
It is assumed that the LCD panel 14 of the LCD 1 has a resolution of (I, J). In other words, the LCD panel 14 includes a pixel matrix including I (I is a natural number) rows and J (J is a natural number) columns. The gradations V(m) include a plurality of gradations V(m, i, j) corresponding to the pixel matrix of the LCD 1, each gradation V(m, i, j) represents a gradation of a number m frame to be provided to a pixel(i, j) located in a number i (1≦i≦I) row and in a number j (1≦j≦J) column of the pixel matrix. The gradations V(m+1) include a plurality of gradations V(m+1, i, j) corresponding to the pixel matrix, wherein each gradation V(m+1, i, j) represents another gradation of a number m+1 frame to be provided to the same pixel(i, j) of the pixel matrix.
The comparator 12 receives the gradations V(m) of the number m frame and the gradations V(m+1) of the number m+1 frame, compares the gradations V(m, i, j) with the gradations V(m+1, i, j), and provides a comparison result to the gradation processor 13.
The gradation processor 13 receives the gradations V(m+1) of the number m+1 frame that are prepared to be displayed on the LCD panel 14, and generates two pairs of compensating gradations according to the gradation V(m+1, i, j) of each pixel. Each pair of compensating gradations includes a primary compensating gradation “A” and a secondary compensating gradation “B”. The gradation processor 13 selects one of the pairs of compensating gradations according to the received comparison result, and then provides the primary compensating gradation “A” of the selected pair of compensating gradations to the LCD panel 14 in an earlier period of the m+1 frame, and provides the secondary compensating gradation “B” of the selected pair of compensating gradations to the LCD panel 14 in a later period of the m+1 frame.
Referring to FIG. 5, is a graph of luminance versus time, showing two luminance curves for the LCD of FIG. 4. Corresponding to each pixel(i, j), the primary compensating gradation 1A and the secondary compensating gradation 1B are respectively equal to the gradation V(m+1, i, j) in the earlier period of a frame and in the later period of the frame. In addition, the primary compensating gradation 2A is greater than the gradation V(m+1, i, j), and the secondary compensating gradation 2B is less than the gradation V(m+1, i, j). An average value of the primary compensating gradation 2A and the secondary compensating gradation 2B is equal to the gradation V(m+1, i, j).
A driving method for the LCD 1 includes the following steps:
step a. providing a plurality of gradations V(m+1) of a number m+1 frame respectively to the frame memory 11 and the comparator 12, and at the same time, providing all the gradations V(m) of the number m frame to the comparator 12 from the frame memory 11;
step b. comparing the gradations V(m, i, j) with the gradations V(m+1, 1, j) respectively corresponding to each pixel by the comparator 12, and providing a comparison result to the gradation processor 13;
step c. when V(m, i, j)=V(m+1, i, j)—in other words, the pixel(i, j) in a number i row and in a number j column displays a still picture in the number m+1 frame—the gradation processor 13 provides the primary compensating gradation 1A to the LCD panel 14 in the earlier period of the number m+1 frame, and provides the secondary compensating gradation 1B to the LCD panel 14 in the later period of the number m+1 frame. When V(m, i, j)≠V(m+1, i, j)—in other words, the pixel(i, j) displays a moving picture in the number m+1 frame—the gradation processor 13 provides the primary compensating gradation 2A to the LCD panel 14 in the earlier period of the number m+1 frame, and provides the secondary compensating gradation 2B to the LCD panel 14 in the later period of the number m+1 frame.
Because the average value of the primary compensating gradation “A” and the secondary compensating gradation “B” is equal to the gradation V(m+1) of the number m+1 frame, the luminance of each pixel of the LCD panel 14 can be maintained to correspond with the input image data. However, when a moving picture is displayed on the LCD panel 14, the primary compensating gradation 2A and the secondary compensating gradation 2B are provided to the LCD panel 14, and a bright picture and a dim picture are sequentially displayed on the LCD panel 14. Thus a viewer may easily perceive flicker of images displayed on the LCD panel 14.
It is desired to provide a new LCD which can overcome the above-described deficiencies. It is also desired to provide a method for driving such LCD.